This invention relates to flow control systems and/or methods of controlling flows and/or equipment including such flow control systems and has been devised particularly though not solely for use in controlling the supply of attemperated water to laundry machines.
The traditional method of providing warm fill water in laundry machines is to pulse a cold water valve on for a given proportion of the fill time. Since the cold flow rate is generally higher than the hot flow rate due to higher cold water pressure, this system works satisfactorily in most domestic situations. It does not, however, provide accurate control since the mix temperature will fluctuate with varying hot pressure, cold pressure, hot temperature and cold temperature. All these can vary from fill to fill to some extent, and from one environment to another to a much greater extent. This is why an adjustment knob (for altering the proportion of cold water to hot water) is usually fitted.
Some machines, particularly in the North American environment where high pressure hot water systems are common, have utilized a bimetal operated proportioning valve--this only works if the flow rates of hot and cold are the same. Most North American machines rely on equal flow rates to provide warm fill at 50% mix by simply turning two conventional valves on together.
It has been realized in the last few years that water temperature is an important factor in wash performance: too cold and soil removal suffers (decreased solubility of wash powder); too hot and fabric damage is excessive. 40.degree. celsius is an accepted optimum warm temperature.
Some home environments have very hot water (80.degree.-90.degree. C.) from "wet back" solid fuel heaters and so on. Control of the hot wash temperature is considered desirable to reduce the excessive hot temperature so that plastics in the machine and delicate clothes placed in the machine are not damaged, clothes wear is limited and risk of burns is reduced. An acceptable hot wash temperature seems to be 60.degree. C.